The present invention relates to manufacturing small electro-mechanical devices, and more particularly, to bonding and packaging of members of Micro-Electro-Mechanical Systems (MEMS) and MEMS based products using a Solid-Liquid InterDiffusion (SLID) bonding process.
Micromechanics, micro-machines, or more commonly, Micro-Electro-Mechanical Systems (MEMS) are an integration of mechanical elements, such as sensors and actuators, and/or electronics on a common substrate through the utilization of micro-fabrication technology. MEMS range in size from a few microns to a few millimeters. While the electronics are fabricated using Integrated Circuit (IC) process sequences (e.g., CMOS, Bipolar, or BICMOS processes), micro-mechanical components are fabricated using compatible xe2x80x9cmicro-machiningxe2x80x9d processes that selectively etch away parts of a silicon wafer or add new structural layers to form mechanical and electromechanical devices.
MEMS bring together silicon-based microelectronics with micro-machining technology, thereby making possible the realization of a complete system-on-a-chip. MEMS augment the computational ability of microelectronics with the perception and control capabilities of microsensors and/or microactuators. Examples of such electrical and mechanical combinations are gyroscopes, accelerometers, micromotors, and sensors of micrometric size, all of which may need to be left free to move after encapsulation and packaging. MEMS may be used within digital to analog converters, air bag sensors, logic, memory, microcontrollers, and video controllers. Example applications of MEMS are military electronics, commercial electronics, automotive electronics, and telecommunications.
In the fabrication of MEMS and other microstructures, two substrates or components may be structurally integrated together, such as by structural bonding. The structural bonds can be provided by any of several bonding techniques known in the art. For example, a direct bond may be formed by joining two clean, polished surfaces together under compressive force. Alternatively, two adjacent solder structures may be integrated and bonded together by reflowing the solder at an elevated temperature. In addition, an anodic bond may be formed between an insulating substrate and a conducting or semi-conducting substrate by the application of a high voltage, such as 1,000 volts, across a junction at an elevated temperature. Structural bonds, such as the aforementioned, are well developed for providing mechanical integration of two or more microstructures. However, a structural bond""s strength may not be effective under harsh conditions. Additionally, these structural bonding methods are each application specific bonding methods and they also may not be viable methods for bonding within a fragile device such as a MEMS.
In some microstructure and MEMS applications, a pressure seal may be desired, such as to isolate a cavity internal to a MEMS or other microstructure from the surrounding environment. Pressure seals may be required, for instance, when a high-pressure gas atmosphere is desired inside a cavity, such as for example, to increase a breakdown voltage threshold used within an electrical component of a MEMS. In other applications, an evacuated cavity may be required, such as for example, for improving a thermal isolation of suspended radiation detectors in a microbolometer. Unfortunately, common structural bonding techniques are generally inadequate to provide pressure sealing because of surface variations and imperfections that preclude the formation of a tight seal across the full extent of a structural bond.
In the packaging of MEMS devices, protection is an important element because corrosion, moisture and debris can prevent the devices from working. Each device should be hermetically sealed, allowing only a negligible amount of gas to be exchanged between the passages in the MEMS body and the atmosphere during the life of the MEMS, in order to prevent the device from becoming contaminated. Existing packaging of MEMS devices typically involve selecting an appropriate arrangement of the MEMS device within a system, selecting an appropriate material for use in bonding the MEMS device in the system, and selecting an appropriate process for applying the material to create a bond. These packaging solutions often involve redesigning a MEMS layout due to materials and processes used, and therefore, are burdensome to accomplish. For example, in a Leadless Ceramic Chip Carrier (LCCC) package, a lid may be soldered to seal the package. However, outgassing may occur when soldering which requires the use of getters to alleviate the outgassing. This results in additional materials, processes, time, and costs.
MEMS packaging presents challenges compared to IC packaging due to the diversity of MEMS devices and the requirement that many of these devices are in continuous and intimate contact with their environment. Presently, nearly all MEMS development efforts must develop a new and specialized package each time a new device is designed. Application specific packaging is not an efficient method of sealing MEMS based products. Consequently, most manufacturers find that packaging is the single most expensive and time-consuming task in a MEMS product development program. Such packaging as wafer level protected MEMS, capped MEMS, and several other types of molded packages have been used by manufacturers. All of these options can be realized in System in Package (SiP) solutions that combine multiple chips and passive devices into one device. These SiP solutions are aimed at reducing the cost of MEMS packaging and providing standardization solutions, however these packaging options may increase the costs of MEMS due to additional design efforts, and since each device requires a specific package, it is believed that the standardization of MEMS packaging can not be realized using known techniques.
One of skill in the art would appreciate a bonding and packaging process that is capable of handling a mass production of MEMS. It would also be desirable to provide a simple process for bonding and packaging MEMS devices to enable design and manufacturing to be completed in a timely fashion and at a low cost.
It would also be desirable to provide a low temperature process for the bonding and packaging of MEMS devices that yields a high temperature and high strength bond. In addition, a selective temperature process for bonding may be desired using materials having different properties such as compositions and melting temperatures.
It would also be desirable to provide a single bonding process for bonding components to MEMS devices and for packaging the MEMS devices in order to simplify the manufacturing process of MEMS devices. For example, a uniform bonding and packaging method is desired for use in approximately all bonds present in a MEMS device.
In view of the above, a method of forming a bond between mating surfaces of members of a Micro-Electro-Mechanical System (MEMS) is provided. The method comprises depositing a first layer of material on a first mating surface. The first layer of material is selected from the group consisting of gold and tin. For example, a material selected from Groups 11 or 14 of the periodic table of elements may be a suitable material with desired properties for bonding. A second layer of material is deposited on a second mating surface. The second layer of material is selected from the group consisting of indium and lead. The first mating surface is pressed against the second mating surface, thereby pressing the first layer of material to the second layer of material. An alloy is formed between the mating surfaces serving as the bond between the first mating surface and the second mating surface of the members of the MEMS.
In another embodiment, a Micro-Electro-Mechanical System (MEMS) is provided including a substrate, a micro-machine coupled to the substrate and a cover coupled to the substrate. The cover and the micro-machine are coupled to the substrate by forming at least one bond between mating surfaces of the cover and the substrate and between mating surfaces of the micro-machine and the substrate. The at least one bond is formed by depositing a first layer of material on a first mating surface. The first layer of material is selected from the group consisting of gold and tin. A second layer of material is deposited on a second mating surface. The second layer of material is selected from the group consisting of indium and lead. The first layer of material is pressed against the second layer of material, thereby forming an alloy to serve as the bond between the first mating surface and the second mating surface of the cover and the substrate and between the first mating surface and the second mating surface of the micro-machine and the substrate.
These as well as other features and advantages of the present invention will become apparent to those of ordinary skill in the art by reading the following detailed description, with appropriate reference to the accompanying drawings.